Presently, available wheelchairs use round wheels which roll very well on smooth floors or on concrete or other paved surfaces which are relatively smooth. The propelling of the wheelchair either by a person or by the use of a motor, however presents great difficulty over uneven or soft terrain, which can be a typical grassy field, or a rocky or sandy area. Teenagers and others do not like to be lifted and carried to the water or onto a beach and would much prefer to have a wheelchair which would enable them to negotiate the rough surface of a beach as well as soft sand. Pebbles or stones act as a block when they hit the wheel of the wheelchair and the soft sand may allow the wheels to sink because of the very narrow surface area under the wheels to support the weight.
Preferably a rough terrain wheelchair would be one which can be readily cleaned if it were pushed fields in which there is mud or sand which can become clogged in the tracks. In addition to being easily cleaned, there is a particular need for such wheelchairs which will be able move across openings or holes in the ground and which will be able to negotiate over small rocks and pebbles without being blocked like the current wheelchair wheels which are often blocked when the user tries to negotiate rough terrain. A further consideration with respect to having a practical wheelchair which may be readily used and adopted is to provide one which is suspended such that the rider will be able to negotiate over small rocks, holes or other obstacles on the rough terrain without tilting to the extent that the occupant will or will fear tipping over. Manifestly, if the wheelchair occupant is alone and is tipped over, he would have great difficulty righting himself and getting the chair back up into its normal upright position. Also, it is preferred that the rough terrain wheelchair have a low profile like that of existing wheelchairs. That is, the wheelchair should not be so elevated that the user is uncomfortable. Thus, the wheelchair should have a low profile and have an independent suspension of the frame and the chair such that the tracks or portions thereof may be deflected at different degrees at the area of the particular rock or projection without tilting the seat and occupant.
In addition to the operating characteristics of a rough terrain wheelchair, it is preferred that the invention include a convertible unit or a retrofit addition to existing wheelchairs, which would allow the user of an existing wheelchair to have attached thereto a track assembly device which could be used over rough terrain and then detached at a later time, either for cleaning or to allow the user to return to the wheelchair to its normal circular wheel locomotion.
Another overriding concern for a rough terrain wheelchair is that it be constructed in an economic manner such that it can be purchased readily by people either for themselves or by other organizations for them.
Accordingly, an object of the present invention is to provide a new and improved wheelchair capable of moving over rough terrain. A further object of the invention is to provide a wheelchair with a retrofit device which will provide a track mechanism allowing the ordinary wheelchair to move over a rough terrain.